A Young River in an Old Valley

The Red River in Minnesota flows backwards in its channel, in a northerly direction. Its course is backwards not because it’s going north (many people in America do think that rivers flow south), but rather, because its channel is part of a larger channel that historically carried more water than any other river on this planet has ever carried. This was the Warren River, which emptied Lake Agassiz (the largest fresh water lake ever) via the Red River Valley, then on to the Minnesota River Valley, then to the Mighty Mississippi. Much mightier then.

Now, the Red River flows north into Lake Winnipeg, which ultimately links to Hudson Bay. It forms the border between North Dakota and Minnesota, passing by Fargo (the very same Fargo that had nothing to do with the Coen brothers’ film of the same name). This region gets a lot of snow some years, and when there is a lot of snow and a quick warm-up in the spring, the river carries quite a bit of extra water. This happens often enough that it is rarely a surprise but nothing close to every year. The flooding, in turn, often causes a great deal of property damage and threatens people’s well being.

We are now seeing thousands of people loading up tens of thousands of sandbags to produce miles of instant levee in the hopes of keeping the river back.

You would expect that if a river floods like this now and then, either people would not live in the flood zones, or the river would be capable of carrying more water. Well, both of those are true, and both of those are in process.

On the people side: People have lived in this valley for about 10,000 years (one of the oldest human skeletons in North America is from a nearby site), and it is almost certain that most of those people, most of the time, knew to avoid the flood zones in the spring. But more recently, different people showed up and they had less experience here. They built towns and eventually cities in the flood plain. Then they got flooded but had already built homes and buildings and roads and stuff. So they rebuilt some things, and in other cases moved, and have slowly improved anti-flooding technologies. Over time, the process of the people of the Red River Valley getting out of the way (and to a smaller extent, adapting to or diverting the floods) will be complete. This will probably take another 100 years. So, that process will have been about a two-century-long process, or about ten generations.

Which would be remarkably fast for humans.

On the river side of it, the river is actually moving an incredible amount of water in an incredibly short time considering that it is essentially flowing upstream. Well, okay, technically it is not really flowing upstream (that would be impossible), but the giant river channel that the Red River flows in is not carved into the landscape to move water north. It is carved into the landscape to move water south. But over the last days of its flow in ancient times (in geological terms, so maybe decades? centuries?), the giant Warren River slowed down its flow and the river channel filled with sediment and clogged up. Whatever rivers are now flowing up (the Red) or down (the Minnesota) this channel of the once greatest river ever are tiny trickles running in irrelevant directions on the top of this sediment.

In other words, the Red River, though it flows in an ancient channel, is pretty much a brand new river on a brand new landscape. In no time at all, the Red River will cut its channel clear of sediment and start eroding into the parent rock, and it will eventually form a deep and wide channel that will easily contain any amount of snow melt.

I’m guessing about ten thousand years. Maybe twenty. But not more than twenty five, anyway.

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on Sunday, March 22nd, 2009 at 6:35 am and is filed under Greg Laden, Science, Seasons.
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The latest thing is to fill heavy-duty plastic bags with water and use them as sandbags. That works only if the current is not too strong or if you can build some kind of framework to hold them in place. But it means a lot less trucking of sand and shovelling, and is easier on the environment.

I had considered including the uplift in this piece as a factor, but it was already a bit too complex. Yes, it is uplifting (at the northern end more than elsewhere, probably) because of rebound. This is not as much as up at Hudson Bay but it is a small factor … but a very small one.

Monado: Thanks for popping over from my other blog! Now, if I can get the other ten of my readers to do this, we’d have something going!

I’d follow Greg anywhere from his blog in some subjects.
Using water in a plastic bag seems to be a strangely counter-intuitive use of the stuff, but have to say, it does make good practical sense when seen for what it is physically. I’ll be interested to see if it’s used this comming spring melt.

I love the idea that most Americans think that rivers flow south! You can see the logic … “Well, the top of the map is North, and the bottom is South and water goes downhill…”.
More seriously, we get people (often large construction companies) building houses on flood plains in the UK, ignoring a thousand years of buildings that are neatly on top of hills. Then you get complaints that “they” haven’t built adequate flood defences. Despite the general dumbing down of society, I think that it’s greed wot duz it, not ignorance.